JP2000264661A - Production of optical fiber preform and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save energy in the secondary drawing working and stabilize the quality of a preform by automatically measuring the diameter, position, etc., of the glass preform before respective steps of drawing, contracting of ends and fire polishing of the glass preform, determining heating conditions, etc., based on the obtained results and continuously automating all the steps. SOLUTION: The diameter of a glass preform is measured in comparison with the position and the drawing speed and heating conditions at respective positions of the glass preform are determined so as to draw the glass preform to a prescribed diameter. Thereby, the glass preform is heated and drawn under the conditions. Markings are placed in joining areas of dummy rods joined to both ends of the glass preform for drawing to measure the positions of the markings, length and diameter of the glass preform are measured after the drawing to determine contracted parts, heating positions and heating conditions. Thereby, contracting of the ends is carried out. The diameter corresponding to the lengths and positions of the contracted parts is measured after drawing and contracting of the glass preform to determine the starting position and completed position of fire polishing and conditions of heating power and carry out the fire polishing. As a result, an optical fiber preform is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for manufacturing an optical fiber preform (hereinafter, referred to as a preform).

[0002]

2. Description of the Related Art Optical fibers for communication and optics are CVD.
It is manufactured by a method, a VAD method, an OVD method, or the like. In these manufacturing methods, usually, first, a glass preform having a diameter of 110 to 200 mm is produced, and then this glass preform is formed to have a diameter 3 to 5 mm larger than the diameter 30 to 100 mm when actually drawing into an optical fiber. The film is primarily stretched to In the primary stretching step, a so-called glass lathe using an electric furnace or a flame burner is used. For a glass base material having a diameter of 100 mm or less, a glass lathe can be used for primary stretching, but for a glass base material larger than this, an electric furnace is generally used because the amount of heat is insufficient with a flame burner. . This electric furnace (stretching device) has about 200
The diameter of the glass preform fed from the top of the furnace heated to 0 ° C. is reduced. Primary stretching in an electric furnace is 5 to 5
The diameter is set to be 10% larger.

[0003] Next, the primary drawn glass base material is subjected to secondary drawing by a glass lathe or the like, and the diameter is precisely adjusted. The secondary stretching is usually performed using a glass lathe in the order of stretching, diameter measurement, drawing at both ends, fire polishing, and finishing diameter measurement. This secondary stretching will be described with reference to FIG. 1, which illustrates the structure of a glass lathe. First, in the stretching, the glass base material A is heated and softened by the burner 3 using the propane gas or the hydrogen gas as the combustion gas and the oxygen as the auxiliary gas to form a molten portion a. By gradually moving 1b (hereinafter referred to as a tail stock) in the pulling direction, the glass base material A is stretched and processed into a target diameter.

Next, the diameter of the glass base material is measured in order to confirm whether the glass base material is in accordance with the final target diameter or the length for the wire drawing machine. Diameter measuring table 2 for diameter measurement
Is used. All the diameter measurements described below are performed by this diameter measuring device 4.

Next, both ends of the glass base material are drawn and processed into a drawn shape as shown in FIG. By using the drawing shape, the drawing process can be easily started. In addition, when the glass base material is set in the drawing furnace, chucking is performed with the dummy rod portion. When the dummy rod is heated and welded to the glass base material, the drawn shape can prevent bubbles from being mixed. When sufficient strength can be obtained, the drawn glass portion may be cut directly by a grinder or the like after the glass base material is directly set and the secondary stretching by the glass lathe is completed.

Next, fire polishing is performed. Heating by a burner of a glass preform during the stretching and squeezing, a part of the glass preform is sublimated becomes SiO, adhere to the existing H _{2 O} again by re glass base material surface become glass particles in the atmosphere , Fogging occurs. In particular, band-like fogging is strongly generated just outside a portion heated strongly by the diaphragm. Although this fogging is glass fine particles, it may be scattered in the drawing furnace to contaminate the furnace atmosphere and damage the surface of the glass base material. So, by performing a fire polish, remove the fogging before drawing,
Strain remaining in the glass base material is set to a level that does not cause any problem.

When the glass base material whose ends are squeezed is fire polished, the strength of the squeezed portions at both ends is low. It becomes difficult to support the glass base material at the end, causing bending or drooping, and in the worst case, falling. Therefore, the operator sets the start position and the end position of the fire polishing according to the diameter and length of the glass base material. This setting is not performed automatically, but is performed based on the operator's own experience. Further, it is necessary to monitor the glass base material for the possibility of occurrence of bending or drooping during fire polishing, particularly when the worker is not a skilled worker. When monitoring a glass base material, an operator needs to be sharp on a glass lathe.

Next, the finished diameter is measured, and the shape of the obtained preform is finally grasped. After that, remove the preform from the glass lathe, melt the drawn area,
The secondary stretching of the preform is completed. A technique has been established in which stretching, fire polishing and diameter measurement are automatically performed by setting a start position and an end position (see Japanese Patent Application Laid-Open No. 60-260429). As for the aperture, recently, a technique for automatically detecting the aperture position and a technique for automatically setting the aperture conditions so as to reduce the processing loss have been reported.

[0009] Each of the above-mentioned steps of the secondary stretching process using a glass lathe can be automatically performed. However, in the case of fire polishing, since the strength of the drawn portion is weak, monitoring is performed during fire polishing. is necessary. In addition, near the end of each process, it is necessary for an operator to go to a glass lathe and perform an operation of setting a start position and an end position of the next process. Since it is necessary to perform such an operation several times for one preform, it has been difficult to save labor in the secondary stretching. In addition, since there are individual differences in setting conditions among operators, it has been difficult to obtain a preform of stable quality.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for manufacturing a preform of stable quality while saving labor in secondary stretching.

[0011]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that an operator does not perform monitoring on a glass lathe and setting of conditions between each process, etc. Draw, measure the diameter before each step of fire polishing, determine the condition setting of each step by computer, stretch, draw both ends, fire polishing,
The present inventors have found that the steps up to the measurement of the finished diameter can be continuously and automatically performed, and have completed the present invention. That is, the method of manufacturing a preform according to claim 1 is
Measure the diameter of the glass base material in correspondence with the position, determine the stretching speed at each position of the glass base material to stretch from the measured diameter and the measurement position to a predetermined diameter, and determine the heating condition from the measured diameter. After the determination, the glass base material is sequentially stretched at the stretching speed while being heated under the heating conditions. In the method for manufacturing a preform according to claim 2, dummy rods for placing the glass base material on the stretching device are joined to both ends of the glass base material, and the joined portions are marked to put the glass base material. After stretching, the position of the marking was detected, the length and diameter of the glass preform were measured, and the drawn portion and the heating position were determined from the detected position of the marking and the length of the glass preform, and measured. The heating condition is determined from the diameter, and the heating position of the drawn glass base material is heated under the heating condition to perform drawing. The method for manufacturing a preform according to claim 3 includes stretching a glass base material,
After drawing, the diameter of the drawn portion and the portion elongated by drawing are measured in correspondence with the position, and the change in the length of the glass base material due to drawing is measured. From the diameter and position and the length of the glass base material, determine the start position and end position of the fire polish and the heating conditions, and extend, from the start position to the end position of the glass base material after drawing, by the heating conditions. It is characterized by fire polishing. Claim 4-
The manufacturing method of the preform of No. 7 is a manufacturing method in which any one or all of claims 1 to 3 are combined. An apparatus for manufacturing a preform according to claim 11, comprising: a heating device movable in the axial direction of the placed glass base material; a diameter measuring device for the glass base material; a traction device for stretching the glass base material; An apparatus for detecting the diameter measurement position of the base material, an apparatus for storing the measured diameter of the glass base material and its measurement position in combination, and for extending the measured diameter of the glass base material and its measurement position to a predetermined diameter. A computing device that determines the stretching speed at each position of the glass base material and determines a heating condition from the measured diameter, a control device that controls the heating device based on the heating condition, and a control device that controls the stretching speed Wherein the glass base material is stretched under the heating conditions and the stretching conditions. 13. An apparatus for manufacturing a preform according to claim 12, comprising: a device for detecting a position of a marking placed at a joint portion between a dummy rod and a glass base material for placing the glass base material on a stretching device; and a glass base material after stretching. A device for measuring the length of the glass preform, a heating device movable in the axial direction of the glass preform and a diameter measuring device for the glass preform, a traction device for the glass preform, and the position of the marking and the length of the glass preform. A storage device for storing, a computing device for determining the drawing portion and the heating position from the position of the marking and the length of the glass base material, a computing device for determining the diameter measurement position for determining the heating condition of the drawing portion, A device for controlling the measurement position, a diameter measurement position and a measured diameter are stored, an arithmetic device for determining a heating condition, and a control device for the heating device are provided, by heating the heating position under the heating condition. Perform aperture And wherein the door. 14. The apparatus for manufacturing a preform according to claim 13, comprising: an apparatus for measuring a change in length of the drawn and drawn glass base material due to drawing; a flame burner device movable in the axial direction of the glass base material; and a glass base material. A diameter measuring device, a device for storing the diameter of the drawn portion of the glass base material and the portion elongated by the drawing and its measurement position in combination, and the length of the glass base material and the drawn portion and the diameter of the portion elongated by the drawing and its An arithmetic device for determining the start position and end position of the fire polish by the flame burner and the heating condition from the measurement position, and a control device for the flame burner device, and the drawing position and the end position of the glass base material after drawing and drawing are set. Up to fire-polishing under the above-mentioned thermal power condition. An apparatus for manufacturing a preform according to a fourteenth aspect is the first aspect.
This is a manufacturing apparatus including all of the apparatuses described in 1 to 13. The preform manufacturing apparatus according to claim 15 is an apparatus for manufacturing a preform according to claim 1.
4 is a manufacturing apparatus provided with a diameter measuring apparatus for measuring a finished diameter of an optical fiber preform after fire polishing in addition to the preform manufacturing apparatus of No. 4.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the production method of the present invention automatically measures the diameter and position of the glass base material before each of the steps of stretching, drawing at the end, and fire polishing. It is characterized in that heating conditions and the like are determined on the basis of the measurement results, and all steps are continuously automated.
The manufacturing method of the present invention is performed using the above-described manufacturing apparatus of the present invention. In the present invention, it is preferable that the heating of the glass base material is performed by a flame burner in stretching, squeezing the ends, and fire polishing. In addition, it is appropriate to cut the markings provided at the joint between the dummy rod and the glass base material for placing the glass base material on the preform manufacturing apparatus.

[0013]

Next, the present invention will be described in detail with reference to examples. The present invention is not limited to the embodiments.

(Example) Diameter 65 mm, length 1000 mm
The glass base material was subjected to secondary stretching by an apparatus of the present invention, which automatically performs all steps of stretching, drawing at an end, fire polishing, and measuring a finished diameter, to produce a preform. A glass dummy rod was set on a rotary chuck provided near both ends of the glass base material, and the glass base material and the glass dummy rod were welded by heating and set in the above-described apparatus. Next, at the joint between the glass base material and the glass dummy rod, a depth of 3 m
An incision of m was made in the entire circumference to complete the setting before stretching. If the operator sets only the start position and end position of the diameter measurement before stretching and the target diameter (60 mm), then the diameter measurement 1, stretching, diameter measurement 2, squeezing of the end, diameter measurement 3, fire polishing, A program was set in the computer to automatically measure the finished diameter. In addition, setting of all conditions such as thermal power conditions in each step can be set by a program input to a computer. That is, the following steps were all automatically performed by the computer. In the diameter measurement 1, the diameter of the glass base material before stretching is measured in accordance with the position, and the stretching speed at each position of the glass base material is determined from the measured diameter and the measurement position,
The heating conditions were determined from the average value of the diameter of the glass base material. Further, the length of the preform after stretching was calculated from the target diameter, and the position of the effective portion of the preform after stretching was calculated from the calculation result. Then, the glass base material was sequentially stretched at the above stretching speed while being heated under the above heating conditions. Then, the position of the effective portion of the preform was accurately confirmed by programming so that the cut made at the joint between the preform and the glass dummy rod before stretching was confirmed by diameter measurement 2. Then, the cut is detected, the length of the glass base material and the diameter of a place 50 mm outside the preform effective portion are measured, and the heating position is determined from the detected position of the cut and the length of the glass base material, The heating condition was determined from the measured diameter, and the heating position of the drawn glass base material was heated under the heating condition and squeezed. In the present embodiment, the program for drawing both ends is set such that the smallest detail has a drawing shape of 20 mm. Also, by installing a scale on the tailstock, the change distance of the length of the preform was calculated. Next, in diameter measurement 3, the diameter of the drawn portion and the portion elongated by the drawing are measured in correspondence with the position, and the change in the length of the glass base material due to the drawing is measured. From the diameter and position, and the length of the glass base material, the starting position and the ending position of the fire polish and the heating condition were determined. Regarding the start position and the end position of the fire polish, as described in [Prior Art], fogging occurs next to a strong flame at the throttle, and no fogging occurs at the narrowed portion. The program was set to be the start and end positions of fire polish. Then, from the start position to the end position of the glass base material after stretching and drawing, fire polishing was performed under the above-mentioned thermal power condition. After the completion of the fire polishing, the finished diameter was automatically measured based on the result of the diameter measurement 3. As described above, the diameter is measured before stretching, drawing, and fire polishing, and the preconditions for the next process, such as the heat power conditions and the setting position of the preform, are accurately set, and all the preforms of stable quality are completely and automatically obtained. Could be produced. In addition, the entire process was performed in about three and a half hours, but the operator did not operate or monitor the lathe at all.

Comparative Example A preform having a diameter of 65 mm and a length of 1000 mm was set on a glass lathe and subjected to secondary stretching in the same manner as in the example. Stretching, drawing, fire polish, and finish diameter measurement were performed automatically.However, before each process was completed, an operator went to a glass lathe and set the conditions for the next process after each process. Monitoring was performed. The entire process of the secondary stretching process took about three and a half hours. Among them, the time when the worker became clear on the lathe was about 50 minutes in total.

[0016]

According to the method and apparatus of the present invention, the diameter and position of the glass base material are automatically measured before each of the steps of stretching, drawing at the end, and fire polishing, and the heating conditions are determined based on the measurement results. Thus, all steps can be continuously automated, and labor saving in the secondary stretching process can be realized. Further, since the conditions for the next process are set based on the calculation results of the computer, the set conditions are always constant, and a preform of stable quality can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view illustrating the structure of a glass lathe.

FIG. 2 is a schematic explanatory view exemplifying a drawn shape of a front end portion of a glass base material.

[Explanation of symbols]

 1a: Rotating chuck 1b: Rotating chuck (tailstock) 2: Moving table for burner and diameter measuring device 3: Burner 4: Diameter measuring device 5: Moving table for rotating chuck (tailstock) A: Glass base material a: Fused portion

Continuation of the front page (72) Inventor Tadakatsu Shimada 2-3-1 Isobe, Annaka-shi, Gunma Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Research Laboratories (72) Inventor Hideo Hirasawa 2-3-3 Isobe, Annaka-shi, Gunma No. 1 Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory F-term (reference) 4G021 BA00

Claims (17)

[Claims] 1. The diameter of a glass base material is measured in correspondence with a position, and the measured diameter and the stretching speed at each position of the glass base material for stretching from the measurement position to a predetermined diameter are determined and measured. A method for producing an optical fiber preform, wherein heating conditions are determined from a diameter, and the glass preform is sequentially stretched at the stretching speed while being heated under the heating conditions. 2. A dummy rod for mounting a glass base material on a stretching device is joined to both ends of the glass base material, and a marking is formed in the joined portion to extend the glass base material. , And measure the length and diameter of the glass base material, determine the narrowed portion and the heating position from the detected marking position and the length of the glass base material, and determine the heating conditions from the measured diameter. And heating the heated position of the drawn glass base material under the above-mentioned heating conditions to perform drawing. 3. After the glass base material is stretched and drawn, the diameter of the drawn portion and the portion elongated by drawing are measured in correspondence with the position, and the change in the length of the glass base material due to drawing is measured. From the diameter and position of the drawn portion and the portion extended by drawing, and the length of the glass base material, the start position and end position of fire polish and the heating conditions are determined, and the starting position of the glass base material after stretching and drawing. A method for producing an optical fiber preform, wherein the process from step to the end position is fire polished according to the heating condition. 4. The production method according to claim 2, wherein the glass base material is stretched by the production method according to claim 1. 5. The production method according to claim 3, wherein the glass base material is stretched by the production method according to claim 1. 6. The production method according to claim 3, wherein the drawing of the glass base material is performed by the production method according to claim 2. 7. The glass base material is stretched by the manufacturing method according to claim 1, the glass base material is drawn by the manufacturing method according to claim 2, and the glass base material is drawn by the manufacturing method according to claim 3. A method for producing an optical fiber preform, comprising performing fire polishing. 8. The method according to claim 1, wherein the glass base material is heated by a flame burner. 9. The method according to claim 2, wherein the glass base material is heated by a flame burner. 10. The method according to claim 2, wherein the marking is a notch. 11. A heating device movable in the axial direction of a placed glass preform, a diameter measuring device for the glass preform, a pulling device for stretching the glass preform, and a position for measuring the diameter of the glass preform. , A device that stores the measured diameter of the glass base material and its measurement position in combination, and a position of the measured glass base material and each position of the glass base material in order to extend from the measurement position to a predetermined diameter. A computing device that determines a heating condition from the measured diameter, a control device that controls the heating device based on the heating condition, and a control device that controls the stretching speed, wherein the heating device An apparatus for manufacturing an optical fiber preform, wherein a glass base material is drawn under conditions and drawing conditions. 12. A device for detecting the position of a marking placed at a joint between a dummy rod and a glass base material for placing the glass base material on a stretching device, and measuring the length of the glass base material after stretching. A device, a heating device movable in the axial direction of the glass base material and a diameter measurement device for the glass base material, a traction device for the glass base material, and a storage device for storing the position of the marking and the length of the glass base material, An arithmetic unit that determines the drawing portion and the heating position from the position of the marking and the length of the glass base material,
An arithmetic device for determining a diameter measurement position for determining the heating condition of the throttle portion, a device for controlling the diameter measurement position, an arithmetic device for storing the diameter measurement position and the measured diameter, and determining the heating condition, An apparatus for manufacturing an optical fiber preform, comprising: a control device for a heating device; and performing drawing by heating the heating position under the heating condition. 13. A device for measuring a change in length of a drawn or drawn glass base material due to drawing, a flame burner device movable in the axial direction of the glass base material, and a diameter measuring device for the glass base material. A device that combines and stores the diameter of the drawn portion of the glass base material and the portion extended by the drawing and its measurement position, and a flame burner based on the length of the glass base material and the diameter of the drawn portion and the diameter of the portion elongated by the drawing and its measurement position. An arithmetic unit for determining the start position and the end position of the fire polish and the heating condition, and a control device for the flame burner device, from the start position to the end position of the glass base material after drawing and drawing, the heating condition An apparatus for producing an optical fiber preform, wherein the apparatus is subjected to fire polishing. 14. Apparatus according to claim 11, and claim 12.
An apparatus for producing an optical fiber preform, comprising the apparatus according to claim 13 and the apparatus according to claim 13. 15. The manufacturing apparatus according to claim 14, further comprising a diameter measuring device for measuring a finished diameter of the optical fiber preform after the fire polishing. 16. The manufacturing apparatus according to claim 11, wherein the heating device is a flame burner. 17. The method according to claim 1, wherein the marking is a notch.
16. The manufacturing apparatus according to 2, 14, or 15.